1 files changed, 120 insertions, 0 deletions
diff --git a/libcxx/include/__memory_resource/monotonic_buffer_resource.h b/libcxx/include/__memory_resource/monotonic_buffer_resource.h
new file mode 100644
index 000000000000..5b0d2462582e
--- /dev/null
+++ b/libcxx/include/__memory_resource/monotonic_buffer_resource.h
@@ -0,0 +1,120 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H
+#define _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H
+
+#include <__config>
+#include <__memory/addressof.h>
+#include <__memory_resource/memory_resource.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 14
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace pmr {
+
+// [mem.res.monotonic.buffer]
+
+class _LIBCPP_TYPE_VIS monotonic_buffer_resource : public memory_resource {
+  static const size_t __default_buffer_capacity  = 1024;
+  static const size_t __default_buffer_alignment = 16;
+
+  struct __chunk_footer {
+    __chunk_footer* __next_;
+    char* __start_;
+    char* __cur_;
+    size_t __align_;
+    size_t __allocation_size() { return (reinterpret_cast<char*>(this) - __start_) + sizeof(*this); }
+    void* __try_allocate_from_chunk(size_t, size_t);
+  };
+
+  struct __initial_descriptor {
+    char* __start_;
+    char* __cur_;
+    union {
+      char* __end_;
+      size_t __size_;
+    };
+    void* __try_allocate_from_chunk(size_t, size_t);
+  };
+
+public:
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource()
+      : monotonic_buffer_resource(nullptr, __default_buffer_capacity, get_default_resource()) {}
+
+  _LIBCPP_HIDE_FROM_ABI explicit monotonic_buffer_resource(size_t __initial_size)
+      : monotonic_buffer_resource(nullptr, __initial_size, get_default_resource()) {}
+
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(void* __buffer, size_t __buffer_size)
+      : monotonic_buffer_resource(__buffer, __buffer_size, get_default_resource()) {}
+
+  _LIBCPP_HIDE_FROM_ABI explicit monotonic_buffer_resource(memory_resource* __upstream)
+      : monotonic_buffer_resource(nullptr, __default_buffer_capacity, __upstream) {}
+
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(size_t __initial_size, memory_resource* __upstream)
+      : monotonic_buffer_resource(nullptr, __initial_size, __upstream) {}
+
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(void* __buffer, size_t __buffer_size, memory_resource* __upstream)
+      : __res_(__upstream) {
+    __initial_.__start_ = static_cast<char*>(__buffer);
+    if (__buffer != nullptr) {
+      __initial_.__cur_ = static_cast<char*>(__buffer) + __buffer_size;
+      __initial_.__end_ = static_cast<char*>(__buffer) + __buffer_size;
+    } else {
+      __initial_.__cur_  = nullptr;
+      __initial_.__size_ = __buffer_size;
+    }
+    __chunks_ = nullptr;
+  }
+
+  monotonic_buffer_resource(const monotonic_buffer_resource&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI_VIRTUAL ~monotonic_buffer_resource() override { release(); }
+
+  monotonic_buffer_resource& operator=(const monotonic_buffer_resource&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI void release() {
+    if (__initial_.__start_ != nullptr)
+      __initial_.__cur_ = __initial_.__end_;
+    while (__chunks_ != nullptr) {
+      __chunk_footer* __next = __chunks_->__next_;
+      __res_->deallocate(__chunks_->__start_, __chunks_->__allocation_size(), __chunks_->__align_);
+      __chunks_ = __next;
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI memory_resource* upstream_resource() const { return __res_; }
+
+protected:
+  void* do_allocate(size_t __bytes, size_t __alignment) override; // key function
+
+  _LIBCPP_HIDE_FROM_ABI_VIRTUAL void do_deallocate(void*, size_t, size_t) override {}
+
+  _LIBCPP_HIDE_FROM_ABI_VIRTUAL bool do_is_equal(const memory_resource& __other) const _NOEXCEPT override {
+    return this == std::addressof(__other);
+  }
+
+private:
+  __initial_descriptor __initial_;
+  __chunk_footer* __chunks_;
+  memory_resource* __res_;
+};
+
+} // namespace pmr
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 14
+
+#endif // _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H